In the manufacture of shingles a mixture of asphalt and limestone or some other suitable inert inexpensive filler (generally referred to as the filled coating mixture) are used to coat the surface of the web prior to the application of the protective granuals. Generally the ratio of asphalt to filler is manually controlled by a proportioning device. To meet government specifications a limited amount of filler may be added and the operator controls the proportioning device to ensure that the resultant mixture does not exceed this upper limit of limestone. Also the mixture must have other characteristics to properly form a shingle during production e.g. viscosity and the operator also adjusts the ratio in the mixture until these characteristics appear to be within specification. However, to ensure that the government regulated amount of limestone is not exceeded requires operation at a level significantly below the maximum level of limestone addition and when the other characteristic requires adjustment for proper operation the amount of limestone is reduced more than required as a safeguard to ensure operation on the equipment.